The present invention relates to a method for determining the progress of internal pressure in a cylinder of an internal combustion engine (1).
To determine the progress of the internal pressure in a cylinder of an internal combustion engine, during the different combustion cycles, it is known that a pressure sensor is located inside the combustion chamber relating to the cylinder. The pressure sensor effects a direct measurement of internal pressure in that it outputs an electrical signal representative of the internal pressure.
The pressure sensors of known type, although allowing a direct time evolution of the internal pressure to the cylinder to be obtained have the disadvantage of being extremely costly, and owing to the hostile conditions of the environment in which they operate, are subject to mechanical and thermal stresses of such a nature as to prejudice their suitable operation in the long term.
Consequently, such pressure sensors are not fitted to volume production engines due to the fact that in the first place they would enormously increase the costs, and in the second place they are likely to provide significant information for a relatively reduced period.
With a view to overcoming such inconveniences an indirect method has been introduced to determine the progress of internal pressure to the cylinder. The method is mainly based on the correlation between internal pressure to the cylinder and the engine block vibrations. In particular the method provides for the use of a piezoelectric accelerometer mounted on the engine block to correspond with the cylinder to generate an electric signal output representative of the engine block vibrations, and the use of a processing system allowing the extrapolation of the pattern of the internal signal from the pattern of the electrical output signal from the accelerometer.
The aforesaid method, notwithstanding the possibility of application to volume-production motor vehicle engines, still has the disadvantage that it requires an external sensor on the engine block (piezoelectric accelerometer) . Installing such sensors on the engine block effectively involves additional cost due to the cost of the sensor itself, as well as the cost of modifications needed by the engine block to provide a seating allowing the sensor to be fitted.